The present invention relates to the field of data-storage devices. More particularly, this invention relates to a method and apparatus for reducing acoustic noise radiated by a disc drive.
Devices that store data are key components of any computer system. Computer systems have many different devices where data can be stored. One common device for storing massive amounts of computer data is a disc drive. The basic parts of a disc drive are a disc assembly having at least one disc that is rotated, an actuator that moves a transducer to various locations over the rotating disc, and circuitry that is used to write and/or read data to and from the disc via the transducer. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved from and written to the disc surface. A microprocessor controls most of the operations of the disc drive, in addition to passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The disc drive includes a transducer head for writing data onto circular or spiral tracks in a magnetic layer the disc surfaces and for reading the data from the magnetic layer. In some drives, the transducer includes an electrically driven coil (or xe2x80x9cwrite headxe2x80x9d) that provides a magnetic field for writing data, and a magneto-resistive (MR) element (or xe2x80x9cread headxe2x80x9d) that detects changes in the magnetic field along the tracks for reading data.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc-drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
An operating disc drive can emit relatively large amounts of acoustic noise generated by vibrations of the disc drive enclosure caused by the pressure from inside air, disturbed by the rotating discs. The spindle and actuator movements create forces that act on the structure of the disc drive. When the forces are applied to the device enclosure, the forces are converted into displacements which in turn create pressure waves in the surrounding air which are perceived as acoustic noise to the human ear.
The actuator assembly moves in response to energizing a voice coil motor to move the actuator assembly around a pivot axis, thereby swinging each of the arms associated with the actuator assembly, the load springs, and associated read/write head over the associated disc surface. When moved in this manner during normal operation, the assembled load springs and associated read/write head tend to vibrate at some frequencies. The spindle motor rapidly spinning the discs contributes additional vibration. Vibration from the spindle motor and movement of the actuator assembly may be transmitted to the disc drive housing through the pivot and spindle journals. The resulting vibration in the housing causes radiation of acoustic noise, especially from the cover. Such acoustic noise may be annoying and may suggest poor quality to the user. There are also standards for acoustic noise that are required by many manufacturers.
The device enclosure actually acts like a radiating surface for the internal forces created by the spindle and actuator movement. The dynamics of the device enclosure, such as the natural modes of vibration, can amplify for the forces generated inside the drive. A frequency chart of disc drive sound power indicates that the highest level of drive noise emission is in the frequency band resulting from the first cover resonance. In this frequency band, the cover loses its efficiency to provide transmission losses to counter act the noise produced by the rotating discs. Moreover, the cover response to forces produced by the voice coil motor (VCM), the actuators, and the spindle motor at the first cover resonance is maximal which results in additional increase in the cover vibration and sound radiation in the above referenced frequency band.
In practice, the first cover resonance takes place in the frequency range of 1000-1500 Hz and its width is about 50-100 Hz depending on the specific design of a particular disc drive. The existing VCM actuators have the first acoustically significant resonance (resonance of arms, coils and yokes) in the vicinity of the first cover resonance. More importantly, if actuator resonant frequencies coincide with the cover resonant frequencies, the additive effect will increase cover vibration and the noise radiated from the disc drive.
As a result, acoustic noise emanating from a disc drive is a critical performance factor that is usually tightly specified to be below a maximum level. As part of the quality assurances practices when manufacturing disc drives, the drives are tested in an acoustic chamber to determine the amount of noise emanating from the device. Drives that emit noise above a maximum threshold need to be reworked to be in compliance with the requirements.
Government agencies throughout the world are now requiring that the decibel level of average sound energy emanating from office equipment be substantially reduced. Computer manufacturers are also placing acoustic emission standards on disc drive manufacturers. Manufacturers of disc drives have also long recognized that certain improvements for data storage performance in disc drives, namely, to increase disc rotation velocity, contribute to unwanted acoustic noise. There is a marked decrease in human sensitivity to acoustic noise below about 200 Hz and above about 6000 Hz. Thus, it is clearly advantageous to attenuate acoustic noise radiated from disc drives in the frequency range from about 200 Hz to about 4000 Hz.
Several methods to reduce the intensity of unwanted acoustic noise have been attempted. Among the several methods are the use of external dampening techniques for the entire disc drive. Some designers have made strides in addressing the acoustic frequencies that escape from the top cover. The designers use cover dampeners and adhesives with inherent dampening properties on the cover. Other designers have attempted to completely surround the exterior of the disc drive with sound absorbing material. Still other designers have attempted to completely isolate the spindle from the base in order to reduce the unwanted acoustic emissions at multiple frequencies. Such spindle isolation conventionally includes indirect attachment of the spindle to the base.
Disc drives are now being contemplated for use in home entertainment applications such as video and television. One application of disc drives includes adding disc drives to home set top boxes. Users in the home entertainment area are especially sensitive to acoustic noise, since noises seem more pronounced during quiet scenes of a movie or when background music is softly played.
Therefore, it is desirable to reduce such acoustic noise. What is also needed is a simple solution that is not prohibitively costly and which introduces few, if any, new parts to the disc drive. Also needed is an inexpensive method and apparatus which only slightly increases the complexity of the manufacturing processes needed to manufacture the drive. The solution also must not increase the size of the disc drive system. What is also needed is a disc drive with fine tuned cover has a first resonance frequency which is separated from the resonant frequency of the actuator. resonances to provide better acoustical performance.
A disc drive system includes a cover that is the prime source of acoustical radiation from the disc drive. The cover includes at least one dampening member provided with a cut or slit therein to shift the resonant frequency of the cover away from other resonant frequencies associated with the disc drive. The cut or slit in the dampening member increases the area with a high value of shear deformation in the adhesive and increases the loss factor to shift the resonant frequency when compared to a cover not having a slit dampening member.
A disc drive includes a base plate and a spindle attached to the base plate. In addition, at least one disc is attached to the spindle and the spindle is adapted to rotate with respect to the base plate. The disc drive also includes a cover for attaching to the base plate. The cover and the base plate form a disc enclosure which encloses the at least one disc and a portion of the spindle. An apparatus for reducing noise produced by the disc-drive system includes a cover having a reduced cover stiffness.
In one embodiment, the cover of the disc drive includes at lease one dampening ring. The dampening ring is cut into at least two portions to reduce the cover stiffness while maintaining approximately the same mass. By cutting the dampening ring, the first resonance frequency of the cover is lowered. As a result of cutting the dampening ring, the first resonance of the cover does not coincide with a resonant frequency of the actuator. As a result, excitation of the cover by the actuator will be less. Cutting the dampening ring will not affect the transmission losses of the cover because the cover mass is the same. It will also affect the damping properties of the cover. It increases the loss factor because of increased area with high value of shear deformation in the adhesive that takes place near the edges (because of the additional inner boundaries as a result of splitting).
In some embodiments the dampening ring is cut more than once. The number of cuts is balanced with the number of pieces produced and adding to the complexity of assembling the disc drive. In other embodiments, other portions of the cover may be cut to reduce the cover stiffness and maintain approximately the same mass.